ITU REGIONAL WORKSHOP ON SMS4DC FOR ENGLISH SPEAKING COUNTRIES IN AFRICA,

ABUJA, NIGERIA , 20-31-MAY 2013

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Propagation Models In SMS4DC

Prepared by :Eng.Yasir Mohammed BasharYasir_192@ntc.gov.sd

Propagation is a term used to explain how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another.

In free space, all electromagnetic waves (radio, light, X-rays, etc.) obey the inverse-square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of the distance from a point source

Doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.

Radio propagation fundamentals

Simplified Description of propagation modes

Point to point communication: Communication provided by a link, for example, radio-relay link between two stations located at specified fixed points

Types of Communications

Point-to-point Radiocommunication Link

Communication provided by links, for example, radio-relay links between single station located at specified fixed point and a number of stations located at specified fixed points.

Point to multipoint communication

Communication provided by links between a station located at a specified fixed point and any number of stations located at non-specified points in a given area which is the coverage area of the station located at the fixed point.

Point to Area communication

Propagation Models In SMS4DC

P.370 VHF and UHF propagation curves for the frequency range 30 -1000 MHz

P.452 Prediction procedure for the evaluation of microwaveinterference between stations on the surface of the Earth atfrequencies above about 0.7 GHz

P.525 Calculation of free space attenuation

P.526 Propagation by diffraction

P.529Prediction methods for the terrestrial land mobile service in theVHF and UHF bands

P.530 Propagation data and prediction methods required for thedesign of terrestrial line-of-sight systems

P.618 Propagation data and prediction methods required for thedesign of Earth-space telecommunication systems

P.1546Method for point-to-area predictions for terrestrial services in thefrequency range 30 MHz to 3 000 MHz

Available sub-items of propagation models in the menu

Unaffected by any consideration other than distance

Free-space waves

Influenced by the action of free electrons in the upper levels of the Earths atmosphere.

Ionospheric waves

Subject to deflection in the lower levels by variations in the refractive index structure of the air through which they pass.

Tropospheric waves

Modified by the nature of the terrain over which they travel.

Ground waves

Radiowave propagation modes

Propagation terms used in SMS4DC(1)Free-spacepropagation

Propagation of an electromagnetic wave in a homogeneous idealdielectric medium which may be considered of infinite extent in alldirections.

Line of sightpropagation

Propagation between two points for which the direct ray is sufficientlyclear of obstacles for diffraction to be of negligible effect.

Radio horizon The locus of points at which direct rays from a point source of radiowaves are tangential to the surface of the Earth.

Troposphere The lower part of the Earth’s atmosphere extending upwards from theEarth’s surface, in which temperature decreases with height except inlocal layers of temperature inversion. This part of the atmosphereextends to an altitude of about 9 km at the Earth’s poles and 17 km atthe equator.

Propagation terms used in SMS4DC(1)Effective Earth-radius factor, k

Ratio of the effective radius of the Earth to the actual Earth radius. For the standard atmosphere, the effective Earth radius is 4/3 that of the actual Earth radius.

Effective antenna height

The effective height of the transmitting antenna is defined as its height over the average level of the ground between distances of 3 and 15 km from the transmitter in the direction of the receiver.

% Time The applicable time percentage values or range of values of the ITU Recommendation; % time is the percentage of time that the predicted signal is exceeded during an average year.

% Location The applicable percent location range of the ITU Recommendation; % location is the percentage of locations within, say, a square with 100 to 200 m sides that the predicted signal is exceeded.

Delta h defines the degree of terrain irregularity

Terrain clearance angle

See diagram in next slides

The Parameter Delta H (Δh)

Terrain Clearance Angle

Some Useful Concepts for Propagation models

Fading :Fluctuation of signal level with respect to stable condition for number of reasons.

Path profile: A vertical cut of terrain along propagation path between transmitter and receiver

NFD: Net Filter Discrimination (NFD) expresses the reduction (in dB) of the interference power if the transmitter and receiver frequencies are different

Polarization: The Locus of Electric field vector fluctuation

Propagation Effects

Diffraction fading due to obstruction of the path; Attenuation due to atmospheric gases; Fading due to atmospheric multipath or beam spreading

(commonly referred to as defocusing) associated with abnormal refractive layers;

Fading due to multipath arising from surface reflection; Attenuation due to precipitation or solid particles in the

atmosphere; Variation of the angle-of-arrival at the receiver terminal and angle-

of-launch at the transmitter terminal due to refraction; Reduction in cross-polarization discrimination (XPD) in multipath

or precipitation conditions; Signal distortion due to frequency selective fading and delay

during multipath propagation.. Attenuation due to sand and dust storms Multipath Fading Cross-polarization discrimination

ITU-R P.370 Intended for prediction of field strength for the broadcasting service for the frequency range 30 to 1 000 MHz and for the distance range up to 1 000 km

Replaced by P.1546 but still used in some bilateral agreementsInput parameters:% Time (range 1 – 50 %): typical 1% for interference contour 50 % for coverage contour% Locations (range 1-99 %): typical coverage contour 99 % interference contour 50 % Δh defines the degree of terrain irregularity; for broadcasting services it is

applied in the range 10 km to 50 km from the transmitter. Typical value = 50 m.

Contour value: appropriate to service type e.g. VHF land mobile fsmin =12dBμV/m

Land/Sea discrimination: if checked will apply correction for % sea/land path

Effective Antenna Height calculation (SMS4DC Tool)

Field strength contour using ITU-R P.370

Select P.370 and Field strength Contour from Propagation Models menu

Select station for contour calculation

P.370 Input parameters

% Time: (1 – 50 %)% Location: (1 – 99 %)Effective radius of the Earth: (k=4/3)System: Analogue/DigitalEnvironment: see inset

Land/Sea discriminationReceiver heightDelta HContour value

P.370: calculation of field strength contours

P.452: Prediction procedure for the evaluation of microwaveinterference between stations on the surface of the Earth at

frequencies above about 0.7 GHz

–N0 (N-units), the sea-level surface refractivity, is used only by the troposcatter model as a measure of location variability of the troposcatter mechanism.

– Delta_N (N-units/km), the average radio-refractive index lapse-rate through the lowest 1 km of the atmosphere, provides the data upon which the appropriate effective Earth radius can be calculated for path profile and diffraction obstacle analysis.

– Beta_e (%), the time percentage for which refractive index lapse-rates exceeding 100 N-units/km can be expected in the first 100 m of the lower atmosphere,

Link calculation

P.525 Calculation of Free Space Attenuation 1

Point-to-area links: If there is a transmitter serving several randomly-distributed receivers (broadcasting, mobile service), the field is calculated at a point located at some appropriate distance from the transmitter by the expression:

where:e : r.m.s. field strength (V/m)p : equivalent isotropically radiated power (e.i.r.p.) of the

transmitter in the direction of the point ind : distance from the transmitter to the point in question (m).

Point-to-point links:With a point-to-point link it is preferable to calculate the free-space attenuation between isotropic antennas, also known as the free-space basic transmission loss (symbols: Lbf or A0), as follows:

where:Lbf : free-space basic transmission loss (dB)d : distanceλ : wavelength

P.525 Calculation of Free Space Attenuation

P.525 Calculation of Free Space Attenuation

P.1546

This Recommendation describes a method for point-to-area radio propagation predictions for terrestrial services in the frequency range 30 MHz to 3 000 MHz

It is intended for use on tropospheric radio circuits over land paths, sea paths and/or mixed land-sea paths between 1‑1 000 km length for effective transmitting antenna heights less than 3 000 m

P.1546

Parameters of different propagation models

Parameters of different propagation models(1)

Parameters of different propagation models(2)

Parameters of different propagation models(3)

P.618 Parameters

Exercising SMS4DC

Step 1 Launch SMS4DC

Step 2: Launch the DEM view using toolbar push button

Step 3 Establish a fix stations A using and set the frequency to 890 MHz

Step 5,6 do the same steps as in 3 and 4 to Establish a fix stations B and set the frequency to 890 MHz

Step 4 Press assign antenna button to chooseantenna “ant_ALE8603_806.ant”

Step 7 Open the administrative part from“Database->licensing”

Step 8: Select “Anonymous Station” and find stationB, open Antenna Information Table of Station B

Step 9 : Push modify button and change the field“class of antenna” from T to C and push save button

Step 10: Find Station A and go to the Frequency tab

and press “Add Receiver” and follow the dialogbox (Choose station B from table under POINT,

andthen close the admin window

Step 11: Open “Database” menu and select “Display Link

Step 12: Select the record of new established hop

Step 13 Open menu “Propagation Model” and select Link item under the ITU-R P.370 propagation model

P.452

P.530

EXCERSISES

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